The invention addresses a polymer coated paperboard which can be utilized for dual ovenable applications. The polymer coating contains a layer of a polyester prepared from at least one of the following monomers: propylene glycol, 1,4-cyclohexanyl dimethylene diol or isophthalic acid. These include poly(1,4-cyclohexanyl dimethylene terephthalate (PCT) or polyethylene isophthalate (PEIT).
In the past, dual ovenable containers have been constructed from a laminate containing paperboard, a tie layer of ethylene-methyl acrylate (EMA), ethylene-vinyl acetate copolymers, acrylic acid copolymers, physical blends of polyethylene with about 20% polyethylene terephthalate (PET) or physical blends of ethylene-methyl acrylate with polyethylene terephthalate. See U.S. Pat. No. 4,455,184.
The polyesters of the present invention are neither discussed nor suggested by the '184 patent. These polyesters have much higher melting points, typically above 250.degree. C. and are more stable than polyethylene terephthalate. This allows the container produced to exhibit superior cooking performance. The superior materials and resultant structures allow for coating weights of the polyester to be below 25 lbs/3,000 sq. ft., something not previously practical with polyethylene terephthalate. Weights below 25 lbs/3,000 sq. ft. of polyethylene terephthalate exhibited poor adhesion to the paperboard substrate, in addition to deleterious pinholes formed therein. Reduction of the coating weights of the product contact layer provided significant economic savings in production of the structure.
It is an object of the present invention to produce a coating for contact with a product in a dual ovenable container that is less costly than polyethylene terephthalate and maintains product quality.
It is a further object of the present invention that reduces coating neck-in during extrusion coating and therefor high trimming and waste.
It is yet a further object of the present invention to increase adhesion of the product contact layer coating to paperboard.
Another object of the present invention is to increase flexibility of the coating structure.
Another object of the present invention is to increase coating line speed without causing detrimental effect on the quality of products being produced.
Yet another object of the present invention is the production of high temperature cooking coated paper containers.